In general, an image pickup apparatus performs white balance adjustment according to a color temperature of a light source. For example, when irradiated under a fluorescent lamp, a white object may be tinged with green, the reflected color. In addition, when irradiated under an incandescent lamp, the white object may be tinged with red, the reflected color. The image pickup apparatus corrects a tone of color through the white balance adjustment such that the object is captured of its image having the original color under this situation. An example of a system which automatically performs the white balance adjustment is an auto white balance adjustment (AWB) system.
The AWB system sets the range of a target color temperature of the white balance adjustment as a color judgment gate. The color judgment gate is a reference for sorting portions, which are originally achromatic colors but tinged with colors under the influence of light, from portions of chromatic colors. The AWB system integrates pixel data sorted based on the color judgment gate for every frame and divides the integration data by the number of integration target pixels, thereby calculating an average value of the pixel data per pixel of each frame. For example, in a case integrating color difference signals, the AWB system obtains a white balance gain to make the calculated average value zero and performs the white balance adjustment. According to a system in the related art, the color judgment gate is set to include various kinds of light source colors from a light source with a low color temperature to a light source with a high color temperature. In this setting, even colors other than the light source color may be included in the sorting target of the color judgment gate. For example, when a colored object with a low chroma such as blue or cyan is captured of its image under the incandescent lamp, since the red of the incandescent lamp and the blue of the object cancel each other out, it looks as if the object is tinged with the achromatic color, so that the object may be considered as one of which the color falls within the range of the color judgment gate. In this example, the white balance adjustment is performed in a state where a slight redness remains. In this way, since the portions tinged with colors other than the light source color are included in the integration target, the white balance adjustment is performed but the ideal white is not accomplished.